Why I keep losing when I win lane and roam?

1-7 and not roaming? no thanks it would be also the end of me if :(

All I can tell you is that when you're ready to snowball, just take an objective after killing 1\2 enemies.. The earlier you can snowball, the more your win will be easy. Never fall behind on CS, always try to reset your lane and push creeps under enemy turret (So your opponent will lose even more, plus adding pressure)

Don't fall behind on cs. Also you may not be taking objectives. Call the shots (baron/dragon/towers). Towers are HUGE, get inhibs and split push if you're zed.

You need to
A. Pick a champ that can carry hardcore.
B. Pick a role that can carry hardcore.
C. Hope you aren't last pick...

If you get forced into supporting just try and emotionally support the team more than anything. Lower ELOs are heavily influenced by the attitude of their teammates.